Pierre Robin (Pronounced Ro-ban) Sequence (PRS) is a condition characterised by the existence of three abnormalities:
- a small or underdeveloped lower jaw (“micrognathia” pronounced micro-nath-ea)
- a cleft palate and an
- upper respiratory breathing obstruction.
Generally, the existence of all three abnormalities together determines the diagnosis of Pierre Robin Sequence. (However it is important to note that recently some babies diagnosed have “high arched” palate's as opposed to clefts).During the very early stages of pregnancy, a foetus’s jaw goes through a rapid growth period. In a child with PRS, this growth is restricted, resulting in the lower jaw being much smaller than it’s expected size.The underdeveloped jaw causes the tongue to become crowded within the mouth. As a result the tongue sits high and is pushed backwards into the airway. The high position of the tongue then interferes with the closure of the palate.The palate is generally formed at around 8-10 weeks gestation, when the two shelves of the palate grow and join at the midline forming the “roof of the mouth”.In infants with PRS, the tongue has been pushed up high into this cavity preventing the joining of the plates, resulting a wide U shaped cleft of the soft and or hard palate.After an infant is born a breathing obstruction also results from the position of the tongue within the mouth. Due to the small jaw, the tongue is also pushed backwards into the airway, resulting in difficulty breathing. This is known as Upper Airway Breathing Obstruction.
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